I've attached a modified version of h5ex_t_vlstring_F03.f90 to use attributes instead. This example assumes you have a F2003 compiler and you used --enable-fortran2003 when you built hdf5. Hope this helps.
Scot
________________________________________
From: Hdf-forum <hdf-forum-bounces@lists.hdfgroup.org> on behalf of Pierre de Buyl <pierre.debuyl@chem.kuleuven.be>
Sent: Wednesday, February 05, 2014 8:59 AM
To: hdf-forum@lists.hdfgroup.org
Subject: [Hdf-forum] VL string attribute in Fortran
Dear hdf community,
I would like to know whether the absence of a "Read / Write Variable Length
String Datatype (Attribute)" is due to a technical problem. The example page [1]
does not provide such an example.
In the context of the H5MD file format [2], we are using (currently) VL string
attributes. If it turns out that we cannot handle those in Fortran, we could
switch to fixed-length strings.
Regards,
Pierre de Buyl
[1] http://www.hdfgroup.org/HDF5/examples/api18-fortran.html
[2] H5MD : HDF5 for molecular data http://nongnu.org/h5md/
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!************************************************************
!
! This example shows how to read and write variable-length
! string attributes to a dataset using h5aread_f and
! h5awrite_f, and F2003 intrinsics C_LOC and C_F_POINTER.
! The program first writes variable-length strings attribute
! Next, it reopens the file, reads back the data, and outputs it to
! the screen.
!
! This file is intended for use with HDF5 Library version 1.8
! and --enable-fortran2003
!
!************************************************************
PROGRAM main
USE HDF5
USE ISO_C_BINDING
IMPLICIT NONE
CHARACTER(LEN=20), PARAMETER :: filename = "h5ex_vlstring_F03.h5"
CHARACTER(LEN=3) , PARAMETER :: dataset = "DS1"
CHARACTER(LEN=2) , PARAMETER :: attribute = "A1"
INTEGER(HSIZE_T), PARAMETER :: dim0 = 4
INTEGER(HID_T) :: file, filetype, space, attr ! Handles
INTEGER :: hdferr
INTEGER(HSIZE_T), DIMENSION(1:1) :: dims = (/dim0/)
TYPE(C_PTR), DIMENSION(1:dim0), TARGET :: wdata
CHARACTER(len=8, KIND=c_char), DIMENSION(1), TARGET :: A = "Parting"//C_NULL_CHAR
CHARACTER(len=8, KIND=c_char), DIMENSION(1), TARGET :: B = "is_such"//C_NULL_CHAR
CHARACTER(len=6, KIND=c_char), DIMENSION(1), TARGET :: C = "sweet"//C_NULL_CHAR
CHARACTER(len=8, KIND=c_char), DIMENSION(1), TARGET :: D = "sorrow."//C_NULL_CHAR
TYPE(C_PTR), DIMENSION(:), ALLOCATABLE, TARGET :: rdata ! Read buffer
CHARACTER(len = 8, kind=c_char), POINTER :: data ! A pointer to a Fortran string
TYPE(C_PTR) :: f_ptr
INTEGER :: i, len
! Initialize array of C pointers
wdata(1) = C_LOC(A(1))
wdata(2) = C_LOC(B(1))
wdata(3) = C_LOC(C(1))
wdata(4) = C_LOC(D(1))
!
! Initialize FORTRAN interface.
!
CALL h5open_f(hdferr)
!
! Create a new file using the default properties.
!
CALL h5fcreate_f(filename, H5F_ACC_TRUNC_F, file, hdferr)
!
! Create file and memory datatypes. For this example we will save
! the strings as C variable length strings, H5T_STRING is defined
! as a variable length string.
!
CALL H5Tcopy_f(H5T_STRING, filetype, hdferr)
!
! Create dataspace.
!
CALL h5screate_simple_f(1, dims, space, hdferr)
!
! Create the attribute and write the variable-length string data to
! it.
!
CALL h5acreate_f(file, attribute, filetype, space, attr, hdferr)
f_ptr = C_LOC(wdata(1))
CALL h5awrite_f(attr, filetype, f_ptr, hdferr )
!
! Close and release resources.
!
CALL h5aclose_f(attr , hdferr)
CALL h5sclose_f(space, hdferr)
CALL H5Tclose_f(filetype, hdferr)
CALL h5fclose_f(file, hdferr)
!
! Now we begin the read section of this example.
!
!
! Open file and attribute.
!
CALL h5fopen_f(filename, H5F_ACC_RDONLY_F, file, hdferr)
CALL h5aopen_f(file, attribute, attr, hdferr)
ALLOCATE(rdata(1:dims(1)))
!
! Read attribute.
!
f_ptr = C_LOC(rdata(1))
CALL h5aread_f(attr, H5T_STRING, f_ptr, hdferr)
!
! Output to the screen.
!
DO i = 1, dims(1)
CALL C_F_POINTER(rdata(i), data)
len = 0
DO
IF(DATA(len+1:len+1).EQ.C_NULL_CHAR.OR.len.GE.8) EXIT
len = len + 1
ENDDO
WRITE(*,'(A,"(",I0,"): ",A)') attribute, i, data(1:len)
END DO
DEALLOCATE(rdata)
CALL h5aclose_f(attr , hdferr)
CALL h5fclose_f(file , hdferr)
END PROGRAM main
